It is known in the art that the alkylation of phenol is an industrially important reaction. The products obtained are either used directly or as chemical intermediates for bulk industries like petrochemicals, fine chemicals, agrochemical etc. The reaction is usually carried out by using liquid Friedel-Crafts catalysts such as AlCl3, BF3, FeCl3 and ZnCl2. The same reaction can also be carried out by making use of a number of catalysts under different conditions and using different alkylating agent in order to get ortho and para alkylphenols.
U.S. Pat. No. 4,267,394 discloses a process involving a reaction of phenol with iso-propanol in the presence of diethyl ether complex of BF3 in phosphoric acid diluent at a temperature range of 70° C. to 90° C. to produce the ortho-isomer.
U.S. Pat. No. 4,532,368 discloses a process for the production of meta and para-alkylphenols from phenol and olefins in the presence of silicalites and ZSM-5 as catalyst at a temperature of 200° C. to 500° C.
U.S. Pat. No. 5,399,786 discloses a process for the preparation tert butyl-p-phenol by the reaction of phenol with alkyl tert-butyl ether in the presence of a protonated strong acid type catalyst in the temperature range of 60° C. to 130° C. and pressure ranging between atmospheric pressure to 5 kg/cm.sup.2.
U.S. Pat. No. 5,475,178 discloses a process for the alkylation of phenol with olefins using phosphotungsticacid supported on MCM-41 at a temperature range of 0° C. to 500° C. degree C. and at a pressure ranging from 0.2 to 250 atmosphere. In the prior art, stress is given to the preparation of the catalyst. MCM-41 is used as a support. For alkylation reaction, olefin is used as an alkylating agent and the reaction is carried out under pressure. Further the process does not claim regeneration of the catalyst. In the present invention, hydrous zirconia is used as a support. The present invention describes the alkylation of phenol with alcohol under atmospheric pressure. Also the present invention describes a simple process for the regeneration of the catalyst. The increased yield, selectivity and catalyst regeneration in the present invention is attributed to the novel reaction conditions, alkylating agent as well as nature of the catalyst support.
U.S. Pat. No. 5,300,703 discloses a process for the selective synthesis of p-nonyl phenol by reacting phenol with olefins in the presence of catalysts selected from the group of 12-tungstophosphoric acid, 12-tungstosilicic acid, 12-molybdosilicic acid supported on an inert oxide such as titanium dioxide, aluminium oxide and silicon oxide. The reaction is carried out at 90° C. under pressure of 100 psi. The maximum % conversion is 91 and the para-nonyl phenol to ortho-nonyl phenol weight ratio is 10.
U.S. Pat. No. 6,204,424 discloses a process for the alkylation of phenol with tertiary-butyl ether and benzyl chloride in the presence of solid acid catalysts such as sulphated oxides of different metals such as Zr, Ti, Fe, Al, Sn and Bi. The catalysts are also reused.
Japanese patents 61251633 and 61200934 disclose the production of highly pure para-tertiary-butylphenol by the reaction of phenol with isobutylene and butene in the presence of activated clay at 10-120° C. and production of the same mentioned product by the reaction of phenol with butene in the presence of aluminium phenoxide and a nitrogen containing base at 30-200° C. respectively.
The prior art processes do not have the advantage of 100% conversion with respect to reaction yield. The present invention has its surprising effect in 100% conversion with respect to reaction yield and 97.2% selectivity with respect to p-tert butylphenol formation.
A number of research papers have been published on the synthesis of alkyl phenol in vapour phase. Selvam and co workers (Catal. Lett. 65, 153, 2000) have reported vapour phase reaction of phenol with tert-butyl alcohol using Fe—MCM-41 at 175° C. They have found 87% selectivity for p-tert-butyl phenol with 21.1% conversion. The same reaction was carried out in presence of sulphated Zirconia (Catal. Lett. 72, 3, 2001) and Al—MCM-41 (Micro. Meso. Mater. 39, 457, 2000) at the same temperature by the same authors.
Sulphated Zirconia and Al—MCM-41 gave 57.8% and 35.9% conversion and 86.5 and 83.4% selectivity for p-tert-butyl phenol respectively.
HY and Hβ were used for the vapour phase reaction of phenol with tert-butyl alcohol at 105° C. and 145° C. respectively by Zhang and Co workers (Appl. Catal. A. 207, 183, 2001; 166, 89, 1998). They have reported 90.4% and 76.3% selectivity for p-tert-butyl phenol with 46.2% and 95.8% conversion for HY and Hβ respectively.
Anand and co workers (J. Mol. Catal. A. 193, 251, 2003) have reported 62.6% selectivity for p-tert-butyl phenol with 45.5% conversion by the vapour phase reaction of phenol with tert-butyl alcohol using Zeolites HY at 170° C.
A number of procedures have also been reported under liquid phase. Samant and co-workers have reported (Appl. Catal. A 276, 5, 2004) liquid phase tert-butylation of phenol in presence of k-10 clay and FeCl3/k-10 clay. The process gives 100% conversion with 62.0% and 66.8% selectivity for p-tert-butylphenol respectively.
V. Hules reported( J. Catal, 218, 249, 2003,) 52.7% conversion with 23.0% selectivity for p-tert-butylphenol using USY catalyst, 54.2% conversion with 80.3% selectivity for p-tert-butylphenol using Zeolite-β, 28.8% conversion with 49.1% selectivity for p-tert-butylphenol using Mordenite, 12.6% conversion with 79.5% selectivity for p-tert-butylphenol using HZSM-5, and 31.5% conversion with 99.3% selectivity for p-tert-butylphenol using H-β as the solid acid catalyst in presence of ionic liquids such as [bmim]PF6, [omim]BF4 and [hmim]BF4.
Y. Shen and co-workers have reported (J. Mol. Catal. A 212, 301, 2004) 44.8% conversion with 49.0% selectivity for p-tert-butylphenol with tungstophosphoricacid supported onto MCM-41 as catalyst.
Of all the reactions described in the art, there is no reaction reported with more than 80% selectivity for p-tert-butylphenol in liquid phase under mild conditions. Although the heteropolyacids are active for alkylation reaction, it is known that deactivation during these reactions is significant.
Especially in alkylation reactions, the catalysts get deactivated due to the coke formation. Traditionally removal of coke from the catalysts was carried out by heating the catalyst at 500° C. The traditional method cannot be applied to the heteropolyacids as they decompose at that temperature.
The present invention describes a novel catalyst regeneration method. The present inventors have for the first time developed a method for regenerating the heteropolyacid by heating at 300° C.
It is known in art that Kozhevnikov has reported (Appl, Catal. A: General 256, 3, 2003) that the recycling of heteropolyacid catalysts is the key issue to their applications. Subsequent regeneration of the same is quite difficult.
The present inventors have surprisingly found that heteropolyacid catalysts can be regenerated and also reused for the same alkylation reaction. The present invention affords a process which is very high yielding and also economically viable as the catalyst can be reused after a simple workup.